1. Field of the Invention
This invention is a method of forming a seal in a confined configuration with a moisture curable, alkoxy-functional room temperature vulcanizing (RTV) composition. The method comprises the steps of: (i) applying to a first substrate comprising a grooved substantially flat surface a moisture curable alkoxy-functional RTV composition; (ii) positioning the grooved substantially flat surface in occluding proximity with a substantially flat surface of a second substrate, so the alkoxy-functional RTV composition effects a seal therebetween; (iii) exposing the alkoxy-functional RTV composition to a detrimental temperature; and (iv) curing the alkoxy-functional RTV composition.
2. Background Information
One of the many uses for moisture curable RTV compositions, is as a formed-in-place gasket (FIPG), such as for sealing automotive engine components. The function of the FIPG is to provide a durable, oil resistant adhesive seal. The RTV composition is applied as a pumpable composition and cures after the parts are assembled. One example would be for sealing the engine oil pan to the engine block. The RTV composition is dispensed directly onto one substrate's flange area and then immediately assembled to the other mating substrate forming a seal between the substrates. In many cases, the RTV composition is in a confined configuration where moisture is very slow to permeate to the center of the flange. Under these conditions it may take several weeks for the RTV composition to cure fully at the center of the flange. Many flange designs call for a groove to be cast into the center of the flange into which the RTV composition is applied. This groove increases the thickness of the RTV composition applied, which further increases the cure time for the RTV composition. Therefore, the RTV composition in a confined configuration can be exposed to engine running conditions, before the RTV composition has fully cured. The automotive manufacturers realize this and have a specific performance test to ensure that the RTV composition will properly cure after being exposed to high temperature during the curing process. Specifically, the performance test requires applying a sealant to a fixture having a 0.004 inch gap to allow moisture permeation and heating the fixture at 130.degree. C. for 100 hours. After heating is stopped, the fixture is taken apart and the sealant is exposed to the atmosphere. To pass the test, the sealant must cure within 24 hours to a rubber consistency.
Moisture curable, RTV compositions used for sealing in confined configurations include those which evolve acetic acid, ketoximes, or amines as by-products during cure. These by-products may corrode the sensitive metals or plastics to which the sealant is bonded. The use of moisture curable sealant compositions which do not have such corrosive by-products produced during cure would therefore be highly desirable.
One potential alternative would be an alkoxy-functional RTV composition, since alkoxy-functional RTV compositions liberate alcohols during cure. However, it appears that alkoxy-functional RTV compositions containing titanium compounds comprising on average less then 3 alkoxy radicals bonded to the titanium, for example a dialkoxyethylacetoacetate titanate chelate, may not cure when the alkoxy-functional RTV compositions are in thick sections, such as in grooves, in a confined configuration and are exposed to elevated temperatures prior to curing. These seals will likely fail after exposure to the elevated temperatures due to inadequate curing.
The present inventors have determined that an alkoxy-functional RTV composition may be used for sealing in a confined configuration which is exposed to elevated temperatures if the alkoxy-functional RTV composition comprises a titanate compound comprising on average at least 3 alkoxy radicals bonded to titanium. For purposes of this invention, a confined configuration is a configuration which inhibits the permeation of moisture and therefore the rate of cure of the alkoxy-functional RTV silicone composition is retarded. In a confined configuration only a very small portion of the alkoxy-functional RTV silicone composition is exposed to a moisture containing atmosphere, when compared to the total volume of alkoxy-functional RTV silicone composition which needs to cure. Some exposure to moisture is necessary for this invention since the alkoxy-functional RTV silicone compositions useful herein require moisture to cure.
The objective of this invention is to provide a method of forming a seal in a confined configuration with an alkoxy-functional RTV composition.